<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>横竖屏</title>

    <style>
        * {
            margin: 0;
            padding: 0;
        }

        body {
            display: flex;
            flex-wrap: wrap;
        }

        div {
            height: 100px;
            background-color: yellow;
            border: 2px solid red;
            box-sizing: border-box;
            width: 33%;
        }

        @media screen and (orientation:portrait) {
            div{
                width: 25%;
            }
        }
        
    </style>

</head>

<body>

    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>

</body>

</html>